core/txpool: additional DoS defense measures

[dwn1998]

Implemented DoS defense schemes

[fjl]

Please provide some additional context about these defense measures. They sure look interesting, it would be nice to hear whether these were explored in a paper or in another implementation!

[tristartom]

We implement a couple of rules restricting transaction admission in the mempool for good. For instance, upon a full mempool, our rule requires discarding an arriving transaction tx if tx is future or tx evicts another transaction to create new future transactions in the mempool. Some of the defensive rules are described in the DETER paper: https://dl.acm.org/doi/pdf/10.1145/3460120.3485369 (or https://tristartom.github.io/docs/ccs21.pdf )

[fjl]

Thanks for the info! This needs to be reviewed by @karalabe and/or @MariusVanDerWijden.

[holiman]

Superseded by #26648